1. Field of the Invention
The present invention relates to printable release compositions for pressure sensitive adhesive articles, such as labels, and to articles containing such release compositions.
2. Description of the Prior Art
Many types of adhesive articles are known, such as labels, tapes, and note pads. Labels, in particular, are used for business forms, files, advertising, and the like. Labels come in a variety of shapes and sizes, such as window labels, machine labels, integrated labels and the like. Integrated labels are physically integrated, during manufacture, with business forms, mailings and the like.
The type of adhesive best suited for use with a particular article depends on the article's ultimate use. The adhesive may be repositionable, permanent or removable. For instance, it may be desirable for some applications to permanently affix an article to an object, for example, a label applied to a file folder. Such applications require a permanent adhesive. A repositionable adhesive, on the other hand, can be applied to an object, removed, and reapplied. Pads of notes, for example, NoteStix or PostIt notes, are examples of articles using repositionable adhesives. CleanTac is an example of a label having a repositionable adhesive. Finally, removable adhesives are appropriate when the article is to be removed after use, but is generally not reusable. Removable adhesives may, however, also include adhesives which become permanent over time.
Regardless of their use, adhesive articles must be stored and readily available for use. Such articles may utilize a separate disposable liner in juxtaposed face-to-face contact with the adhesive substrate with a release material coated on the side of the liner in contact with the adhesive side of the adhesive substrate. Just prior to use, the liner is peeled away from the adhesive. Such an adhesive article is often referred to as a "linered" label. Alternatively, the adhesive article may be a substrate coated on one side with a release material and coated on the opposite side with an adhesive material. Such a linerless label can be stored in pads or rolls.
The release coating facilitates either the removal of the adhesive-coated substrate from the liner or the pad or the unwinding the linerless label from the roll. The release coating needs to have sufficient adhesion to keep, for example, the linered label on its backing, or the linerless label on a pad or in a roll, but must have sufficient release properties to allow the label to be removed from the backing or pad or to be unwound from the roll, while maintaining its adhesive property.
For some time there have been problems in producing a release coating that possesses the above properties and that, additionally, contains printed matter. One problem relates to retaining the tenacity of the printed matter on the substrate so that the printed matter is not pulled off by the adhesive or wiped off by contact occasioned by someone rubbing against or applying the label. Another problem is "fill-in" of letters such as "o", "a", "e", etc. Fill-in occurs when the porosity of the substrate is not sufficient to absorb the ink and the ink has a tendency to feather out. Wipe-off and related problems may occur if the porosity of the substrate is too low and the ink does not dry sufficiently.
As an example of the above-mentioned problems, a release coating may be used for the printing of Postnet barcodes and FIM codes for automated mail processing. Postnet (Numerical Encoding Technique) is used to encode the ZIP code or ZIP+4 code on an envelope and is located in the lower right portion of a mail piece. FIMs (Facing Identification Marks) are used to identify Business Reply Mail and are a series of vertical bars printed in the upper middle portion of the mail piece just to the left of the postage indicia. FIMs greatly facilitate the automated processing of the mail; thus the quality and placement of the barcodes is very critical to the success of automated processing techniques. For instance, in a linerless label application, the barcode or barcodes are printed on the release surface of a substrate. If feathering or wipe off of the printed indicia occurs, then the information contained in the respective barcodes cannot be scanned. This may result in the loss of the cheaper bulk mailing rate. Standard postage for each piece must then be paid, increasing the cost to the customer, and the mail must be mechanically sorted, causing delay.
In the case of thermal transfer printing, not only is a high surface energy preferred, but the surface must be very smooth. Most thermal substrates contain clay coatings with relatively high surface energy and bending properties to enhance ink transfer and anchorage. A release coating imparts a lower surface energy to the face of the label for better release characteristics, making printing much more difficult. Thus, higher surface energy provides higher print quality, whereas lower surface energy provides for better release characteristics. Thus, there is a need for a printable release coating having both a good quality print and good release characteristics.